1. Field of the Invention
The present invention relates to an electrothermal integrator and an audio frequency filter and, more particularly, to an electrothermal integrator and an audio frequency filter having thermally-isolated electrothermal structures.
2. Description of the Prior Art
Electrothermal structures fabricated by micro-machining technology have been employed in a variety of types of sensors. An electrothermal structure is a structure in which there is thermal interaction between its electrical components. As an example of the application of the electrothermal structure, Euisik Yoon et al. proposed a fluid velocity sensor utilizing an electrothermal structure on page 1376 of the IEEE Transaction on Electron Devices (June 1992), and also proposed a RMS-DC converter utilizing a diaphragm structure on page 1666 of the IEEE Transaction on Electron Devices (September 1994). In addition, Richard J. Reay et al. proposed a bandgap reference circuit utilizing an electrothermal structure fabricated by way of electrochemical etching in the International Solid State Circuit Conference of 1995, and obtained U.S. Pat. No. 5,600,174 directed to this technology on Feb. 4, 1997.
Integrated circuit filters typically used switched capacitor filters, or continuous time filters utilizing transconductance amplifier-capacitor (xe2x80x9cGm-Cxe2x80x9d) integrators. However, an audio-frequency low-frequency filter utilizing a Gm-C integrator requires a large capacitor, such that the integration of the capacitor on the chip becomes difficult. In addition, an audio-frequency low-frequency filter utilizing a switched capacitor filter has problems such as switching noise and aliasing.
Therefore, it is an object of the present invention to provide an electrothermal integrator for audio frequency filters having an insulated electrothermal structure that is fabricated by way of micro-machining technology so that the above problems associated with conventional audio frequency filters can be solved. It is another object of the present invention to provide an audio frequency filter as an application of the insulated electrothermal structure fabricated by micro-machining technology.
To this end, the electrothermal integrator for the audio frequency filter according to an embodiment of the present invention comprises a transconductance amplifier for receiving a first voltage signal and converting the first voltage signal to a current signal, and an electrothermal structure for receiving the current signal output from the transconductance amplifier, converting the current signal to a temperature signal, and converting the temperature signal to a second voltage signal.
Here, the electrothermal structure comprises a substrate having an aperture formed thereon, an insulator layer formed on the substrate and covering an opening of the aperture, a heater formed on the insulator layer over the opening of the aperture, the heater converting the current signal input from the transconductance amplifier to the temperature signal, and a sensor formed on the insulator layer over the opening of the aperture and separated from the heater, the sensor converting the temperature signal of the heater to the second voltage signal.
The electrothermal structure may also be formed by comprising a substrate having a groove formed on a surface thereof, an insulator layer formed on the surface of the substrate, the insulator layer having an extended portion extending over the groove, a heater formed on the extended portion, the heater converting the current signal input from the transconductance amplifier to the temperature signal, and a sensor formed on the extended portion and separated from the heater, the sensor converting the temperature signal of the heater to the second voltage signal.
The audio frequency filter according to a first embodiment of the present invention has an electrothermal structure for converting a first electrical signal received as an input signal to a temperature signal and for converting the temperature signal to a second electrical signal, an input signal processing circuit for inputting the first electrical signal to the electrothermal structure, and an output signal processing circuit for outputting the second electrical signal converted by the electrothermal structure, wherein the electrothermal structure comprises a substrate having an aperture formed thereon, an insulator layer formed on the substrate and covering an opening of the aperture, a heater formed on the insulator layer over the opening of the aperture, the heater converting the first electrical signal input from the input signal processing circuit to the temperature signal, and a sensor formed on the insulator layer over the opening of the aperture and separated from the heater, the sensor converting the temperature signal of the heater to the second electrical signal.
The audio frequency filter according to a second embodiment of the present invention has an electrothermal structure for converting a first electrical signal received as an input signal to a temperature signal and for converting the temperature signal to a second electrical signal, an input signal processing circuit for inputting the first electrical signal to the electrothermal structure, and an output signal processing circuit for outputting the second electrical signal converted by the electrothermal structure, wherein the electrothermal structure comprises a substrate having a groove formed on a surface thereof, an insulator layer formed on the surface of the substrate, the insulator layer having an extended portion extending over the groove, a heater formed on the extended portion, the heater converting the first electrical signal input from the input signal processing circuit to the temperature signal, and a sensor formed on the extended portion and separated from the heater, the sensor converting the temperature signal of the heater to the second electrical signal.
The audio frequency filter according to the third embodiment of the present invention comprises a first transconductance amplifier for receiving a first voltage signal and for converting the first voltage signal to a first current signal, an electrothermal structure for receiving the first current signal output from the first transconductance amplifier, converting the first current signal to a temperature signal, and converting the temperature signal to a second voltage signal, and a second transconductance amplifier for converting the second voltage signal to a second current signal, the second current signal being feedbacked to an input of the electrothermal structure.
Here, the electrothermal structure is the same as those used in the electrothermal integrator of the present invention.
The audio frequency filter according to a fourth embodiment of the present invention comprises a first transconductance amplifier receiving a first voltage signal and converting the first voltage signal to a first current signal, a first electrothermal structure for receiving the first current signal output from the first transconductance amplifier, converting the first current signal to a first temperature signal, and converting the first temperature signal to a second voltage signal, a first amplifier for amplifying the second voltage signal output from the first electrothermal structure, resulting in a third voltage signal, a second transconductance amplifier for converting the third voltage signal output from the first amplifier to a second current signal, the second current signal being feedbacked to an input of the first electrothermal structure, a third transconductance amplifier for receiving the third voltage signal output from the first amplifier and for converting the third voltage signal to a third current signal, a second electrothermal structure for receiving the third current signal output from the third transconductance amplifier, converting the third current signal to a second temperature signal, and converting the second temperature signal to a fourth voltage signal, a second amplifier for amplifying the fourth voltage signal output from the second electrothermal structure, and a fourth transconductance amplifier for converting the fourth voltage signal output from the second amplifier to a fourth current signal, the fourth current signal being added to the second current signal and feedbacked to the input of the first electrothermal structure.
Here, the first and second electrothermal structures are the same as those used in the electrothermal integrator of the present invention.